AIC1577 AIC [Analog Intergrations Corporation], AIC1577 Datasheet - Page 8

• Manufacturer Part Number: AIC1577
• Description: External NMOS Step-Down PWM Controller
• Manufacturer: AIC [Analog Intergrations Corporation]

Introduction
AIC1577 is a current mode switching regulator con-
troller
MOSFET with constant frequency architecture. It
uses external divider to adjust output voltage with
excellent line regulation and load regulation. A
maximum high duty cycle limit of 95% provides low
dropout operation, which extends operating time in
battery-operated system.
Wide input voltage ranges from 4.5V to 24V, and
switching frequency (500KHz) allows smaller sized
filter components. The operating current level is
user-programmable via an external current sense
resistor and it automatically enters PFM operation
at low output current to boost circuit efficiency.
PIN DESCRIPTIONS
APPLICATION INFORMATION
PIN 1: CS
PIN 2: I
PIN 3: FB
that
TH
/RUN -Combination of error amplifier
drives
- Current sense comparator invert-
- Feedback error amplifier input, to
ing input, not to exceed V
age. Built in offsets between the
CS and V
with R
thresholds.
compensation point and run con-
trol inputs. The current compara-
tor threshold increases with this
control voltage. Forcing this pin
below 0.8V causes the device to
be shutdown.
compare the feedback voltage
with the internal reference voltage.
Connecting a resistor R2 to con-
verter output node and a resistor
R1 to ground yields the output
voltage:
V
OUT
external
=0.8 x (R1+R2)/ R1
SENSE
IN
set the current trip
pins in conjunction
N-channel
IN
power
volt-
A multifunction pin (I
compensation plus shutdown. A built-in soft start
can properly provide sequence supplies. Available
packages are in SOP8 and MSOP8 for SMD.
Principle of Operation
AIC1577 uses a current mode with a constant fre-
quency architecture. Normally high-side MOSFET
turns on each cycle when oscillator sets RS latch
and it turns off when internal current comparator re-
sets RS latch. Voltage on I
output voltage of voltage error amplifier, will control
peak inductor current. The output voltage feeds
back to V
a voltage through external resistor divider. When
load current increases, it causes a slight decrease
PIN4: GND - Singal GND for IC. All voltage lev-
PIN 5: SW
PIN 6: DRI
PIN 7: BOOST - Supply to high-side floating
PIN 8: VIN
FB
pin so that the error amplifier receives
- Switch node connection to induc-
- External
- The chip power supply pin. It also
els are measured with respect to
this pin.
tor. In buck converter applications
the voltage swing at this pin is
from a schottky diode voltage
drop below ground to V
gate drive pin. Connect DRI to
gate of the external high-side N-
MOSFET.
driver. The bootstrap capacitor C3
is returned to this pin.
provides the gate bias charge for
all the MOSFETs controlled by
the IC. Recommend supply volt-
age is 4.5V~24V.
TH
TH
/RUN) allows external
high-side
/RUN pin, which is the
AIC1577
N-MOSFET
IN
8